Typically, patients with heart failure have a reduced capacity for myocardial function. The heart is unable to adequately meet the metabolic demands of the body by providing the appropriate blood flow. This may result in increased blood pressure (afterload), and increased volume retention (preload). Thus, common symptoms of ventricular dysfunction or heart failure include fatigue, which is caused by the low cardiac output, and edema and swelling, which is caused by fluid overload.
Current guidelines for the evaluation and management of chronic heart failure (HF) tend to focus on the presentation of subjects while they are awake. However, several recent studies have shown that sleep disordered breathing (SDB), commonly known as sleep apnea, may play an important role in the pathogenesis and progression of heart failure.
The prevalence of undiagnosed sleep apnea in the U.S. is thought to be in the millions with on the order of 2% of middle-aged women and 4% of middle-aged men having sleep apnea syndrome. See Young T. et al., “The occurrence of sleep-disordered breathing among middle-aged adults,” New England J. Med. 1993; 328:1230-1235. Sleep apnea is a condition that results from a reduction in air intake through the air passage of sleeping individuals. This problem arises as a result of weak muscle tone in the throat and, although compensated for during waking hours, gives rise to symptoms of fatigue during the day, poor quality sleep at night, and heavy snoring during sleep. Diagnosis of sleep apnea has been carried out in sleep laboratories where the patient is monitored at night during sleep in a process called nocturnal polysomnography. This diagnostic test is expensive, time consuming, and must be administered by highly trained technicians. Consequently, availability of the test is limited.
Sleep disordered breathing (SDB) is estimated to occur in about 60% of patients suffering from congestive heart failure (CHF; Rechtschaffen A, Kales A, eds. A Manual of Standardized Technology, Techniques and Scoring System for Sleep Stages of Human Subjects. Los Angeles: UCLA Brain Information Service/Brain Research Institute, 1968). Nasal continuous positive airway pressure (CPAP) has been advocated as a nonpharmacological treatment for patients with congestive heart failure and certain forms of SDB.
The clinical implications of SDB are not widely recognized and are seldom taken into account in the evaluation and management of heart failure (HF). The conventional approach to the evaluation and management of HF may need to be modified in view of a growing body of evidence showing that the acute and chronic mechanical, hemodynamic, autonomic, and chemical effects of SDB place subjects with HF at increased risk of accelerated disease progression. A convenient method of screening heart failure patients for the presence of SDB is therefore desired.